1. Field of the Invention
The present invention relates to a method and a device for combining auxiliary and main stacks in a delivery or feeder of a machine for processing printing materials, having a motor driven rake that can be moved in and out between the auxiliary and main stacks and having a control computer for controlling driving of the rake. The invention also relates to a sheet-fed offset printing press having the device.
The delivery and the feeder are important constituent parts of sheet-fed offset printing presses. While the feeder is used to supply new printing materials, the delivery accepts sheets printed in the printing press and stacks them on one another. Both in the feeder and in the delivery, the stack has to be changed from time to time since, after a certain amount of time, the stacked sheets in the feeder have been used up, while in the delivery, after a certain amount of time, there is no longer any space for new printed sheets. The changing of the stack in the feeder or delivery of a sheet-fed offset printing press can be carried out by the press being switched off and in each case the stack in the feeder and delivery being removed and a new one introduced. However, since a stoppage of the press is uneconomical, what is known as nonstop operation has become widespread, both in the feeder and in the delivery in sheet-fed printing presses. During nonstop operation, the changing and introduction of a new stack in the feeder or delivery takes place with the press running, which requires appropriate technical measures. During nonstop operation, there are aids in the feeder and in the delivery which make it possible to handle two stacks simultaneously. To that end, for example in the feeder, when the sheet printing materials are disappearing, a rake is moved in under the small residual stack and lifts the residual stack off the actual stack carrying board. The printing materials on the rake are generally designated as an auxiliary stack. Since, in that case, the residual printing materials rest on the rake and no longer on the stack carrying board, the stack carrying board can be moved downward and can accept a new stack. When a new stack has been introduced on the stack carrying board, that new stack, which is also designated as a main stack, has to be combined with the residual stack continuing to shrink continuously on the rake. That combining of the main stack and the auxiliary stack is done by the rake under the auxiliary stack being pulled out again, so that the sheet printing materials of the auxiliary stack are deposited on the main stack. Such combining must proceed as gently as possible in order to ensure that the printing materials are not damaged.
A similar method in nonstop operation is applied in the delivery, but in the opposite order, in that, with a full main stack, first of all a rake is introduced above the main stack and, for a short time period, intercepts further printed sheets. The main stack underneath the rake can then be removed from the delivery and, instead, an empty pallet can be moved in. Following the introduction of the empty pallet into the delivery, that empty pallet is moved up and positioned under the rake, so that the auxiliary stack in the delivery can be deposited on the empty pallet. Following the removal of the rake under the auxiliary stack, the delivery continues to operate as before and accepts the finished printed sheets. Devices for automatic stack change in nonstop sheet feeders or deliveries are basically known. Such a nonstop device is known, for example, from German Utility Model DE 20 2004 017 813 U1. In that case, the nonstop device operates semiautomatically, since in that case the action of pulling out the supporting rods between the main stack and the auxiliary stack is performed through the use of a motor, while the action of pushing in the supporting rods must continue to be carried out manually. That semiautomatic embodiment is more economical than a fully automatic embodiment, since in that case only a pulling device for the supporting rods of the rake have to be provided but no thrust drive in order to be able to position the rake under the auxiliary stack. However, since such a semiautomatic nonstop device continues to need manual intervention, it is not suitable for fully automatic nonstop operation on the feeder or delivery of a sheet-fed printing press. In addition, there is also the risk of operating personnel damaging sheets when pushing the supporting rods under the auxiliary stack of the feeder, since the pushing in action can take place only by utilizing the sense of touch of the operating personnel. German Published, Non-Prosecuted Patent Application DE 41 29 165 A1, corresponding to U.S. Pat. No. 5.529,456, discloses a device for combining a residual sheet stack and a main sheet stack in a nonstop feeder. In that case, during the combining of the residual sheet stack with the main sheet stack to form an overall stack, a rake is pushed in through the use of a drive motor. The rake and its lattice bars have a specific cross section at its free rod ends, in order to prevent the residual sheet stack from sagging during combining. That is intended to permit fault-free combining of the main and auxiliary stacks in the feeder. However, since an extremely wide range of materials can be processed in sheet-fed printing presses, in the case of a fully automatic embodiment, the same procedure of automatic pushing in and pulling out of the rake is currently carried out. In that case, markings can occur on sheets, which then have to be removed from the stack as rejects.